Age, period, and cohort effects on gender differences in alcohol use and alcohol use disorders in 47 national, longitudinally-followed cohorts Project abstract: Available evidence suggests that, across the lifecourse, gender patterns in alcohol use and alcohol use disorders are converging; however, (a) whether this convergence depends on developmental stage, (b) whether it is due to more rapid increases among women compared with men or, conversely, more rapid decreases among men compared with women, and (c) why it is happening all remain inadequately understood - representing a critical knowledge gap. Indeed, intervention and prevention efforts require information about whether convergence is limited to certain age groups, and most critically, why they occur. Further, potential increases in drinking among women portend a potential public health crisis, requiring accurate forecasting of future burden. Without such information, intervention and prevention efforts can be misplaced, focusing on the wrong age groups, or the wrong mediating factors. Only data with sufficient variation both historically and developmentally can answer foundational questions about diminishing gender differences in alcohol-related outcomes. Drawing from a lifecourse perspective, the present project will leverage 47 longitudinal cohorts collected through the Monitoring the Future (MTF) project, from 1976 through 2022, and apply rigorous age-period-cohort growth curve modeling to illuminate: when in historical time and during what developmental periods from ages 18 to 45 gender patterns have been converging; how gender patterns are converging (i.e. because women are increasing, men are decreasing, or both), and why gender patterns are converging. To determine why we will examine an unprecedented array of potential mediating factors including sociological trends in role transitions (marriage, parenthood, education, residential independence, and employment), gender and societal attitudes, and psychological factors (drinking attitudes and reasons, future intentions for partnership and parenthood, parenting and marriage satisfaction). We will employ rigorous age-period-cohort growth models to accomplish three aims: (1) Test when in historical time and at what developmental age gender patterns in alcohol consumption, binge drinking, and alcohol use disorder symptoms are converging or have converged; (2) Forecast future public health burden of alcohol consumption, binge drinking, and alcohol use disorder symptoms and (3) Analyze sociological, psychological, and attitudinal factors as potential mediators of gender convergences across historical time and developmental age. Mediation will be estimated with novel methods developed for epidemiological applications that overcome problematic assumptions of previous approaches. MTF data have been a key source of information on substance use for more than four decades; studies have not to date been used to examine age- period-cohort trends in gender differences in alcohol consumption. When, how, and why gender differences in alcohol consumption vary across both the lifecourse and generations represents an important gap in the literature; our proposed use of MTF data stands to be a seminal contribution.